Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 5 Oct 2021 12:28:27 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Mel Gorman <mgorman@techsingularity.net>,
        Mike Galbraith <efault@gmx.de>, Ingo Molnar <mingo@kernel.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Barry Song <song.bao.hua@hisilicon.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to
 nr_running
Message-ID: <YVwoy30GY61Z4nid@hirez.programming.kicks-ass.net>
References: <20210920142614.4891-3-mgorman@techsingularity.net>
 <22e7133d674b82853a5ee64d3f5fc6b35a8e18d6.camel@gmx.de>
 <20210921103621.GM3959@techsingularity.net>
 <ea2f9038f00d3b4c0008235079e1868145b47621.camel@gmx.de>
 <20210922132002.GX3959@techsingularity.net>
 <CAKfTPtCxhzz1XgNXM8jaQC2=tGHm0ap88HneUgWTpCSeWVZwsw@mail.gmail.com>
 <20210922150457.GA3959@techsingularity.net>
 <CAKfTPtB3tXwBZ_tVaDdiwMt-=sGH1iV6eUV6Rsnpw7q=tEpBwA@mail.gmail.com>
 <20210922173853.GB3959@techsingularity.net>
 <CAKfTPtDc39fCLbQqA2BhC6dsb+MyYYMdk9HUvrU0fRqULuQB-g@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKfTPtDc39fCLbQqA2BhC6dsb+MyYYMdk9HUvrU0fRqULuQB-g@mail.gmail.com>
Precedence: bulk

On Wed, Sep 22, 2021 at 08:22:43PM +0200, Vincent Guittot wrote:

> @@ -7161,6 +7162,13 @@ static void check_preempt_wakeup(struct rq *rq,
> struct task_struct *p, int wake_
>                 return;
> 
>         update_curr(cfs_rq_of(se));
> +       delta_exec = se->sum_exec_runtime - se->prev_sum_exec_runtime;
> +       /*
> +        * Ensure that current got a chance to move forward
> +        */
> +       if (delta_exec < sysctl_sched_min_granularity)
> +               return;
> +

I think we tried that at some point; IIRC the problem with this is that
if the interactive task fails to preempt, that preemption is lost. IOW
interactivity suffers.

Basically if you don't want wake-up preemptions, use SCHED_BATCH, then
those tasks will not preempt one another, but the SCHED_NORMAL tasks
will preempt them.